Condenser bushing



April 28, 1931. G. A. BURR CONDENSER BUSHING Filed Jan. '10. 1929 INVENTOR Gordon A Bur/r ATTORNEY Patented Apr. 28, 1931 UNITED STATES PATENT OFFICE GORDON A. BURR, OF WILKINBBUBG, PENNSYLVANIA, ASSIGNOR IO WESTINGHOUSE ELECTRIC fi uANU l'AcTUBilNG COMPANY, A CORPORATION 'OF PENNSYLVANIA CON DENSEB BUSHING Application filed January 19, 1929. Serial No. 331,583.

My invention relates to electrical bushing structures and particularly to bushings of the, condens er type.

One object of my invention is to provide a bushing, of the above-indicated character, in which the power loss, in the form of heat therein, as compared to similar bushings heretofore employed, shall be greatly reduced.

Another object of my invention is to materially reduce the quantity and weight of material required for condenser bushings of given voltages.

Another object of my invention is to provide a condenser structure that shall employ aslightly porous but relatively dense dielectric-layer material and a binder therefor that shall not penetrate the layer surface beyond a certain depth.

A further object of my invention is to pro- 4 vide a condenser or bushing structure that shall be simple and durable in construction, economical to manufacture and effective in its operation.

Heretofore, it has been customary, in highvoltage bushing practice, to construct a bushing of alternate relatively thin conducting and dielectric layers or cylinders of successively greater diameters and lesser lengths to provide nearly uniform capacity between the conducting layers and to impose substantially uniform stress on the dielectric layers.

However, .for relatively high voltages, the number of layers in, and the radius of, the bushing become so great that, under alternating high-voltage stresses, there is a considerable power loss, in the form of heat. This loss has been a troublesome problem and a material limitation as to the kinds of apparatus and the values of voltage that could be safely, economically and commercially employed.

This heat-power loss, under alternating high-voltage stresses, apparently occurs in all solid and fluid dielectric materials and,

since the solid material cannot dissipate its heat by convection, the heat must be conducted to the -surface and radiated.

It ist'herefo're, important and necessary, if

lcondensers' simi'lar to that of'my invention are to be rendered more effective and adapted for high-voltage service, that the dielectric losses shall be reduced and the dielectric strength increased.

Condenser bushings have been improved from time to time by taking advantage of ad to be almost unbelievable to those skilled in this field.

In the past, the preferred dielectric, over which no improvement has been made or sug-' gested, so far as I am aware, has consisted of a porous paper treated with a binder, such as shellac or similar resinous material. Further treatment of the shellacked paper, under heat and pressure, caused the shellac to penetrate entirely through the paper and apparently left no voids or gas pockets therein.

All theory and laboratory tests of those most interested andbest versed in this art indicated that the above porous paper and its treatment to eliminate voids and gas pockets was the mostefl'ective method of obtaining low dielectric losses and high dielectric strength and was essential to the production of a bushing having the desired dielectric properties.

In accordance with my discovery, the above-mentioned voids and gas pockets apparently do not have any adverse effect, provided they are sufficiently minute and evenly distributed.

Instead, therefore, of employing a highly porous paper having pronounced voids and gas pockets and being subject to complete, or nearly complete, penetration by the shellac, I emplo a relatively dense paper which, while su ciently porous-.to securely gri the binding material, is not enetrated there y to any great depth. In ot er words, while the binder or shellac may penetrate the dielectric to a sufiicient depth to obtain an effective bond therewith, there is a stratum or layer, intermediate the opposite surfaces, of the dielectric layer, that is free of the binder.

Contrary to the usual expectations that voids and gas pockets would adversely affect the structure, it has been found that, in a bushing constructed in accordance with my invention, the internal loss per unit volume is reduced to approximately one fifth the value obtained by the former structure.

This very surprising result permits a higher electrostatic stress to be safely employed, reduces the radius of the bushing and the quantity of dielectric material in a condenser for a given voltage service, lowers the cost of manufacture and transportation charges, saves storage and operating space, permits desirable improvements in co-operating apparatus and has other advantages, such as reduction of labor and facility of handling.

Figure 1 of the accompanying drawing, is a side view, partially in elevation and partially in section, of a condenser bushing embodying my invention.

2 is an enlarged detail sectional View of a portion of the structure, as viewed at the upper right hand portion of Fig. 1, and

Figs. 3 and 4 are similar cross-sectional views, on a greatly magnified scale, offragments of the paper formerly employed and that employed in my invention, respectively, illustrating in a diagrammatic way, the relative.densit1es and'degrees of penetration by the binder. \I

The device comprises, in general,-a central through conductor 2 and a plurality of a1- ternate conducting and dielectriccylinders or layers 3 and 4, respectively.

The layers 3 and 4 are of successively outwardly greater diameters and lesser lengths to provide nearly equal capacities or any desired grading of capacities between-the conducting layers 3.

This arrangement results in a structure, as

shown in Fig. 1, having an intermediate 'cy-' lindrical body portion 6 and tapered or stepped end portions 7 and 8, respectively.

The intermediate portion 6 is for mounting'the bushing in an opening in a, tank cover and the end portions 7 and 8 may be of any desired relative lengths in accordance with the service for which they are adapted and of the medium in which they are to operate.

The conducting layers may be of any suit able material, such as lead or tinfoil, but are preferably of embossed aluminum foil havin one or both surfaces treated or coated with a binder, such as shellac.

The dielectric layers'4, although illus- I trated in Figs. 1 and 2 for clearness as comthe spirit and scope eral layers of paper, each layer being provided on one or both sides thereof with a binder similar to that on the conducting layers 3.

The layers 3 and 4 are preferably prepared vin advance, as above described, with the shellacked surfaces applied thereto and dried.

These layers are then wound under heat and pressure, causing the shellac to momentarily soften and to permanently harden,

trated or impregnated with the shellac, as

indicated by the stippling in Fig. 3.

Fig. 4 is a similar view of the more dense paper which does not permit the shellac to penetrate it very deeply, as indicated by the stippling. However, 1; e penetration or adherence is sufiicient to provide a bond between the several la ers thereof and between the paper and the oil that is as effective as in the prior practice.

This paper. is preferably of such density,

in a sheet of substantially 5 mils thickness and onesquare inch area, that it requires one hundred and thirty-five seconds, or a greater time, to pass 'one hundred cubic centimeters of air therethrough under a constant pressure of approximately twenty ounces avoirdupois.

This density of paper insures that the paper will remain free of the resin, as to its interior pores, and, as above stated, effects the surprisin result of reducing the dielectric loss to a out twenty per cent or less of that existing in the lpenetrable or porous pa or previously emp oyed.

s an exam le of the resultsv attained from this constructlon, a bushing for 220,000-volt service of materia ,and it is estimated that a bush-" ing for 330,000-volt service ,may be constructed as a standard commercial structure at a saving of one-half the quantity of material, with other attendant economies and advantages. These results are premised upon actual test and performance of bushings now being. commercially used to of the former type. v

While I have shown and described a particular'form of my invention, changes may be effected therein without departing from thereof, as set forth in supersede those the appended claims,

I claim as my invention 1. A condenser including a conducting be constructed at'a saving of aplayer, a flexible dielectric layer and a binder between the layers, the binder penerating the dielectric layer but only to a suflicicnt depth to be effectively secured thereto.

2. A condenser including a conducting layer, a fibrous dielectric layer and a binder between the layers, the dielectric layer having a stratum intermediate its surfaces substantially tree of the binding material.

3. A condenser including a conducting layer, a fibrous dielectric layer and a binder between the layers that only slightly penetrates the dielectric layer.

4. A condenser including a conducting layer, a paper dielectric layer and a binder therebetween, a space between the surfaces of the paper being substantially free of penetration by the binder;

- 5. A condenser including alternate flexible layers of conducting and dielectric materials held together by a binder which penetrates the dielectric material only to a*1'ela tively slight depth relative to the thickness thereof.

6. A condenser including a conducting layer and a dielectric layer of flexible material having a porosity corresponding to a porosity, in a sheet of the material of ap-' proximately five mils thickness and one square inch area, requiring more than one hundred and thirty-five seconds to pass one hundred cubic centimeters of air under a constant pressure of approximately twenty ounces avoirdupois therethrough.

7. A condenser bushing including concentric alternate layers of conducting and dielectric materials, the latter consisting of paper having a porosity corresponding to a porosity, in a sheet of the material of approximately five mils thickness and one square inch area, requiring more than one hundred and thirty-five seconds to pass one hundred cubic centimeters of air under a constant pressure of approximately twenty ounces avoirdupois therethrough.

8. A condenser including a conducting layer, a paper dielectric layer and a layer of shellac between said layers that penetrates the paper layer by less than one-half the distance therethrough.

9. A condenser bushing including concentric alternate layers of conducting and dielectric materials, the latter consisting of paper having a porosity corresponding to a porosity, in a sheet of the material of ap- 10. A condenser bushing including concentric alternate layers of conducting and dielectric materials, the latter consisting of paper having a porosity corresponding to a porosity, in a sheet of the material of approximately five mils thickness and one square inch area, requiring more than one hundred and thirty-five seconds to pass thercthrough one hundred cubic centimeters of air under a constant pressure of approximately twenty ounces avoirdupois.

11. A condenser including a conducting layer and a dielectric layer having a stratum parallel to, and between, its sur aces solely of paper.

12. A condenser including a conducting layer and a dielectric layer embodying a stratum parallel to, and between, its surfaces, solely of paper, the Voids in which are of substantially uniform size and distribution throughout.

In testimony whereof, I have hereunto subscribed my name this 8th day of January, 1929. v

GORDON A. BURR.

proximately five mils thickness and one square inch area, requiring more" than one hundred and thirty-five seconds to pass one hundred cubic centimeters of air under a constant pressure of approximately twenty ounces avoirdupois therethrough, and a binder for holding the layers-together which penetrates the paper but only to a sufiicient extent to hold the paper to the conducting material. 

